299 lines
7.4 KiB
C
299 lines
7.4 KiB
C
#include "parse.h"
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#include <ctype.h>
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#include <limits.h>
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#include <stdbool.h>
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#include <stddef.h>
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#include <string.h>
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#include "ast/ast.h"
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#define UNREACHABLE() __builtin_unreachable()
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#define ARR_SIZE(Arr) (sizeof(Arr) / sizeof(*Arr))
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#define OP_STRING(...) (const char[]){__VA_ARGS__}
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#define OP_SIZE(...) (sizeof(OP_STRING(__VA_ARGS__)) - 1)
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static const struct {
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const char *op;
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const size_t op_len;
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const enum op_kind kind;
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const int prio;
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const enum { ASSOC_LEFT, ASSOC_RIGHT, ASSOC_NONE } assoc;
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const enum { OP_INFIX, OP_PREFIX, OP_POSTFIX } fix;
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} ops[] = {
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# define OP(Kind, Prio, Assoc, Fix, /* Operator string */ ...) \
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{ OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), Kind, Prio, Assoc, Fix, },
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#include "operators.inc"
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};
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static struct ast_node *climbing_parse_internal(const char **input, int prec);
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static struct ast_node *parse_operand(const char **input);
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static void eat_char(const char **input)
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{
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*input += 1; // Skip this character
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}
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static void skip_whitespace(const char **input)
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{
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while (*input[0] && isspace(*input[0]))
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eat_char(input);
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}
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static size_t parse_binop(size_t *op_ind, const char **input)
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{
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skip_whitespace(input);
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size_t best_len = 0;
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for (size_t i = 0; i < ARR_SIZE(ops); ++i)
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{
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if (ops[i].fix != OP_INFIX) // Only look at infix operators
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continue;
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if (ops[i].op_len <= best_len) // Only look at longer operators
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continue;
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if (strncmp(*input, ops[i].op, ops[i].op_len) == 0)
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{
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best_len = ops[i].op_len;
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*op_ind = i;
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}
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}
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// Return how many characters should be skipped
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return best_len;
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}
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static size_t parse_prefix(size_t *op_ind, const char **input)
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{
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skip_whitespace(input);
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size_t best_len = 0;
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for (size_t i = 0; i < ARR_SIZE(ops); ++i)
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{
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if (ops[i].fix != OP_PREFIX) // Only look at prefix operators
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continue;
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if (ops[i].op_len <= best_len) // Only look at longer operators
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continue;
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if (strncmp(*input, ops[i].op, ops[i].op_len) == 0)
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{
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best_len = ops[i].op_len;
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*op_ind = i;
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}
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}
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// Return how many characters should be skipped
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return best_len;
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}
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static size_t parse_postfix(size_t *op_ind, const char **input)
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{
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skip_whitespace(input);
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size_t best_len = 0;
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for (size_t i = 0; i < ARR_SIZE(ops); ++i)
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{
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if (ops[i].fix != OP_POSTFIX) // Only look at postfix operators
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continue;
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if (ops[i].op_len <= best_len) // Only look at longer operators
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continue;
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if (strncmp(*input, ops[i].op, ops[i].op_len) == 0)
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{
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best_len = ops[i].op_len;
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*op_ind = i;
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}
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}
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// Return how many characters should be skipped
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return best_len;
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}
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static int right_prec(size_t op_ind)
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{
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if (op_ind >= ARR_SIZE(ops))
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return INT_MIN; // Defensive programming
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if (ops[op_ind].assoc == ASSOC_RIGHT)
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return ops[op_ind].prio;
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return ops[op_ind].prio + 1;
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}
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static int next_prec(size_t op_ind)
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{
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if (op_ind >= ARR_SIZE(ops))
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return INT_MIN; // Defensive programming
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if (ops[op_ind].assoc != ASSOC_LEFT)
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return ops[op_ind].prio - 1;
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return ops[op_ind].prio;
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}
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/*
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* Simple climbing parser, see `operators.inc` for more details.
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*
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* Whitespace is ignored in the input string, only serving to delimit numbers.
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*
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* The input shall consist of a single expression, having a trailing
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* expression in the input results in an error.
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*/
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struct ast_node *climbing_parse(const char *input)
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{
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if (input == NULL)
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return NULL;
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struct ast_node *ast = climbing_parse_internal(&input, 0);
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if (ast == NULL)
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return NULL;
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// Make sure there is no trailing character, except whitespace
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skip_whitespace(&input);
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if (input[0] != '\0')
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{
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destroy_ast(ast);
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return NULL;
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}
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return ast;
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}
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static size_t update_op(size_t *op_ind, bool *is_binop, const char **input)
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{
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skip_whitespace(input); // Unnecessary given that both methods skip it...
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const char *save_input = *input;
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size_t op_bin;
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size_t bin_size = parse_binop(&op_bin, input);
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// Reset the parsing
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*input = save_input;
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size_t op_post;
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size_t post_size = parse_postfix(&op_post, input);
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// Reset the parsing
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*input = save_input;
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if (bin_size > post_size)
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{
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*op_ind = op_bin;
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*is_binop = true;
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return bin_size;
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}
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else if (post_size > bin_size)
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{
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*op_ind = op_post;
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*is_binop = false;
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return post_size;
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}
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// NOTE: assume that there were no matching operators at all, instead
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return 0;
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}
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static bool prec_between(size_t op_ind, int min, int max)
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{
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if (op_ind >= ARR_SIZE(ops))
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return false; // Defensive programming
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return min <= ops[op_ind].prio && ops[op_ind].prio <= max;
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}
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static struct ast_node *climbing_parse_internal(const char **input, int prec)
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{
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prec = prec;
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struct ast_node *ast = parse_operand(input);
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int r = INT_MAX;
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size_t len = 0;
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size_t op_ind; // Used in the next loop
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bool is_binop; // Used in the next loop
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while ((len = update_op(&op_ind, &is_binop, input)) // Initialise the operator
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&& prec_between(op_ind, prec, r) // Use newly initialized operator
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&& ast)
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{
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*input += len; // Skip the parsed operator
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if (is_binop) // Given to us by `update_op`
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{
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struct ast_node *rhs =
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climbing_parse_internal(input, right_prec(op_ind));
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if (!rhs)
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{
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destroy_ast(ast);
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return NULL;
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}
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struct ast_node *tree = make_binop(ops[op_ind].kind, ast, rhs);
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if (!tree)
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destroy_ast(ast); // Error case
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ast = tree;
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}
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else
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{
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struct ast_node *tree = make_unop(ops[op_ind].kind, ast);
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if (!tree)
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destroy_ast(ast); // Error case
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ast = tree;
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}
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r = next_prec(op_ind);
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}
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return ast;
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}
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static bool my_atoi(const char **input, int *val)
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{
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if (!isdigit(*input[0]))
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return false;
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*val = 0; // Initialize its value
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do
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{
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*val *= 10;
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*val += *input[0] - '0';
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*input += 1;
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} while (isdigit(*input[0]));
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return true;
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}
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static struct ast_node *parse_operand(const char **input)
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{
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struct ast_node *ast = NULL;
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int val = 0;
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size_t skip = 0;
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size_t op_ind;
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if ((skip = parse_prefix(&op_ind, input))) // Removes whitespace as side-effect
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{
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*input += skip; // Skip the parsed operator
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ast = climbing_parse_internal(input, next_prec(op_ind));
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if (!ast)
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return NULL;
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struct ast_node *tree = make_unop(ops[op_ind].kind, ast);
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if (!tree)
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destroy_ast(ast);
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ast = tree;
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}
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else if (my_atoi(input, &val))
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ast = make_num(val);
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else if (*input[0] == '(')
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{
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// Remove the parenthesis
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eat_char(input);
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ast = climbing_parse_internal(input, 0);
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// Check that we have our closing parenthesis
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skip_whitespace(input);
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if (*input[0] != ')')
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{
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destroy_ast(ast);
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return NULL;
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}
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// Remove the parenthesis
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eat_char(input);
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return ast;
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}
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return ast;
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}
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